Central vision is essential to activities, such as reading or driving, where visual detail is of importance. Central vision impairment (CVI) is due to damage to the macula, the portion of the retina responsible for central vision, and can be due to a variety of pathological conditions, including macular degeneration, diabetic retinopathy, etc. Of these, macular degeneration (MD) is a disease of the eye, which is very common. There is no cure for MD and visual aids, such as special spectacles or implanted intraocular lenses, are often employed to assist the patient suffering from MD. There are many deficiencies with these methods. Note that although this disclosure discusses MD specifically, the various disclosed embodiments, however, can also apply to CVI in general without limitation to the cause of CVI.
FIG. 1 illustrates a schematic diagram of the horizontal cross-section of a human eye 10, showing the retina and macula with respect to a visual axis 11. The cornea 17 and lens 15 of the eye 10 are also shown in FIG. 1, in addition to the fovea 19. In general, the retina 13, or light-sensitive region of the eye, contains the macula 21, which is the region of the retina 13 responsible for central vision. Although the macula 21 occupies less than 5% of the area of the retina 13, it is essential for any close-inspection activities such as reading. Macular degeneration (MD) is a disease of the eye (e.g., eye 10 shown in FIG. 1), which can damage part or all of the macula 21. Sufferers of macular degeneration typically retain some level of peripheral vision, so they can usually perform some normal activities such as walking. They cannot, however, perform any task requiring central vision such as reading. They are unable to use their peripheral vision for such tasks, since the obscured region of view moves with their gaze.
FIG. 2(a) illustrates a pictorial view of a simulation 20 of the field of view of a person suffering from some forms of macular degeneration, wherein the central vision region is obscured corresponding to the diseased portion of the retina. FIG. 2(b) illustrates a similar simulated view 21 but for a more complicated condition, wherein the central vision region is obscured as well as distorted, corresponding to the diseased portion of the retina. FIG. 2(c) and FIG. 2(d) illustrate simulated representations 22 and 23 of image deformation from similar forms of macular degeneration, represented in terms of an Amsler grid, which is commonly used in diagnosing MD. FIGS. 2(a)-2(d) thus illustrate how the sight of a person suffering from MD might be obscured and/or distorted. The obscured and/or distorted region of the image moves as the person looks at different objects, thereby always degrading the critical region of interest.
Age-related macular degeneration (AMD) is a commonly-occurring form of MD and is prevalent in older people. According to a WHO report [1], the number of visually impaired persons worldwide was 161 million, of which 8.7% (e.g., 14 million) suffered from AMD. The rate of occurrence in developed countries, with their older populations, is significantly greater, up to, for exmple, approximately 20%. Moreover, when other forms of MD and other eye diseases, which result in similar disabilities, are considered, the numbers are even greater.
Medical intervention includes pharmaceutical drugs and surgical procedures such as laser photocoagulation. Some of these have been shown to retard progression of the disease, but there is no effective cure for MD.
The primary form of treatment involves the use of vision aids which divert some of the incident light to the undiseased peripheral portion of the retina. These vision aids range from special spectacles to implantable intraocular lenses.
Special spectacles are commercially available, but they do not always work well and they can be expensive. Moreover, each pair of spectacles is typically for a specific task (e.g., reading) and unsuitable for other tasks (e.g., driving). MD is a progressive disease which gradually (or sometimes rapidly) gets worse. Such spectacles consequently need to be frequently replaced.